The gag (Mycteroperca microlepis) is one of the most important commercial and recreational fisheries in the southeastern United States and Gulf of Mexico. This study responds to questions about the efficacy of creating spatial or temporal marine reserves of spawning aggregations of gag and other groupers in order to ensure their long-term sustainability. In order to make such a determination, research is needed regarding the degree of dispersal among spawning aggregation habits of gag grouper. The major objectives are: (1) to test the hypothesis that 2005 spawning aggregations in the southeastern US (i.e., Florida vs. South Carolina vs. North Carolina) are genetically distinct; (2) to test the hypothesis that postlarvae entering S.C. and N.C. estuaries were generated by spawning aggregations offshore S.C. and N.C. in 2005; and, (3) to provide a preliminary test of the hypothesis that there is temporal genetic structure by comparing the genetic diversity of 2005 spawning adults, 2005 S.C. postlarvae, and a 20-year-old archived collection of S.C. postlarvae. We also propose to use these data to estimate the effective population size (Ne) of gag in the southeastern US.
Study results will provide insight to fisheries managers in South Carolina and with the South Atlantic Fishery Management Council on whether spawning aggregations of gag in the southeastern United States waters (i.e., eastern Florida into North Carolina) should be considered a panmictic single population or a series of relatively independent aggregations. The implications of these alternatives for marine reserve design are profound. In particular, if evidence shows that postlarvae entering South Carolina waters were generated from spawning aggregations offshore South Carolina, this might provide impetus for protecting local aggregations. Evidence that South Carolina postlarvae are produced by non-South Carolina aggregations would support broad protection measures throughout the southeastern U.S. Atlantic shelf.